This invention relates generally to adhesion promotion and, more specifically, to a process for promoting the adhesion between polymeric resists and gold surfaces and to articles made thereby.
In the fabrication of certain articles, a radiation sensitive layer of material is patterned and then used as a process mask in subsequent process steps. For example, in the fabrication of semiconductor devices, radiation sensitive layers of etch resistant material are used to pattern both semiconductor substrates and the material present on the substrates. A layer of radiation sensitive polymeric resist material is formed overlying the substrate and is exposed either optically or using an electron beam or soft x-rays to form patterns of exposed and unexposed resist. Depending upon the type of resist material used, either the exposed or unexposed areas are removed to leave an etch resistant pattern on the substrate. The resist mask is then used as an etch mask to etch a carefully controlled pattern in the material underlying the resist. To closely replicate the resist mask the resist must remain adherent to the underlying material during the etching process. If the patterned resist layer does not adhere, in its entirety, to the underlying surface, the etchant will encroach under the lifted resist and the pattern will not be replicated.
To insure that the resist layer adheres to the underlying material, it has become conventional with some underlying materials to use an adhesion promoter. Silane coupling agents, for example, are well-known when the underlying material comprises a mineral surface such as silicon dioxide or an aluminum metal surface. Silane coupling agents promote polymer adhesion to the underlying mineral surface through a chemical interaction with surface silanol defects encountered at the surface. Analogous surface defects, aluminols ##STR1## are present on an oxidized aluminum surface and good adhesion to this surface is achieved by chemical interaction between adhering polymeric films and the surface defects. The common adhesion promoters which provide satisfactory adhesion between resist and either mineralized or aluminum surfaces generally fall in the category of halogenated alkoxy or amino silanes.
In some articles, including, for example, bubble memory devices and some semiconductor devices, especially advanced bipolar circuits, RF transistors, and very high performance, high density integrated circuits, there is a need for patterned gold metallization. The gold metallization, especially in contrast to aluminum metallization, is very resistant to chemical corrosion, is much less prone to electromigration effects, and provides a high conductivity electrical interconnection. When using gold as the metallization layer, and especially where metal patterns involve lines of width less than 2-3 micrometers, it becomes imperative that the polymeric resist have excellent adhesion to the gold surface. Heretofore, however, there has not been a process for achieving satisfactory adhesion between polymeric resist materials and gold surfaces. The conventional adhesion promoters which are satisfactory for aluminum or mineral surfaces are not effective with gold surfaces. The difference between gold and either aluminum or mineral surfaces is apparently that gold has a drastically different surface; gold does not possess surface adhesion promoting defects because it is a noble metal and is essentially corrosion and oxidation resistant. While the surface of aluminum, for example, is known to be easily chemically oxidized, gold is not oxidized even under oxygen plasma conditions.
It is therefore an object of the present invention to provide an improved process for enhancing the adhesion of polymeric resist materials to gold surfaces.
It is a further object of this invention to provide a process for lithographically patterning gold layers on a semiconductor device.
It is a still further object of this invention to provide an improved article having a layer of patterned gold metallization.
It is a still further object to provide an improved semiconductor device.
It is yet another object of this invention to provide an improved process for fabricating a semiconductor device.